Tectonic structures developed in Oligocene limestones: Implications for New Zealand plate boundary deformation in North Canterbury

Abstract

Abstract Systematic analysis of brittle and semibrittle tectonic structures developed in two Oligocene limestones provides a good record of the post middle Cenozoic low‐strain deformational history in North Canterbury. These structures imply two periods of deformation. (1) Mild mid‐late Oligocene shortening along a NNE horizontal axis is inferred from fractures at a low angle to bedding. These are widespread throughout the northeastern South Island and indicate a regional tectonic event associated with the distal effects of major Oligocene extension in western New Zealand. (2) Late Pliocene ‐ Recent shortening was associated with the development of orthogonal fracture sets (many containing stylolites), macrofractures, small‐scale faults, and macroscopic folding. The late Cenozoic deformation is characterised by northwest‐southeast shortening, which is locally overprinted by east‐west and north‐south shortening associated with folding and the activation of macroscopic faults in basement. These late Pliocen...